I'm done with puberty (chest hair, facial hair, shoulders and height have not grown in 2 years), can I still obtain hip growth?
The bones may not stretch, but fat displacement can still occur. When you see folks with really big hips, often its fat.
The difference in size and shape of the hip bones contributes more to leg angles than hip size, like was said, hip size is fat, and that'll be part of HRT, estrogen causes fat collection there. You can get halfway there for leg angles too though, the bones won't change shape, but I've heard reports of the tilt of the hips changing to the feminine position after a good while on HRT, which while it doesn't get you all the way there makes an enormous difference.
I originally forgot to mention that muscles contribute to thighs too, you can get decent even without hrt of you're diligent about exercises for thigh and butt